Portable computers must be small, light, and sturdy yet have as large a data storage capacity as possible within the limits of these restrictions. The big obstacle to achieving this goal is the heat generated by the computer components. Various methods of cooling by ventilation have been attempted. A variable speed fan has been used, the speed of which varies with the temperature. It has also been proposed to provide air flow in a modular housing each containing modular electronic components by causing the fan to operate at a higher speed if the temperature in any of the modular compartments exceeds a threshold temperature.